Brazing is a process where a first material is joined to a second material by a third material, the brazing material. The brazing process typically includes a preparation step where the surfaces of the first and second materials that are to be brazed to one another are cleaned to remove oxides and the like that can adversely affect the integrity of any braze joint subsequently established between the first and second materials. Typically, the surfaces are cleaned by etching or removing the outermost layer of each of the surfaces. Once cleaned, the first and second materials can be brazed to one another. To achieve a high quality braze joint between the first and second materials, brazing must occur in an oxygen depleted atmosphere to inhibit the formation of oxides on the surfaces on the first and second materials that can reduce the ability of the brazing material to wet or adhere to the surfaces. Typically, the oxygen depleted atmosphere is achieved by using a flux that decomposes at or near the melting point of the brazing material and establishes an atmosphere around the surfaces of the materials being brazed that is substantially free of any oxygen.
The process of brazing a metal to a ceramic is extremely sensitive to oxidation. Consequently, it is generally carried out in a vacuum furnace where the vacuum and the flux cooperate to achieve the oxygen depleted atmosphere adjacent to the surfaces of the metal and the ceramic that is necessary to achieve a reliable braze joint. Presently, however, the ability to braze a metal to a ceramic is limited to situations where the surfaces of the metal and the ceramic have a high degree of exposure and, as a consequence, present relatively little resistance to the establishment of the requisite oxygen depleted atmosphere. There are situations, however, where the surfaces of the metal and the ceramic are not exposed enough for the flux and the vacuum of the furnace to establish the necessary oxygen depleted atmosphere. An exemplary situation is where the metal object must be brazed into a recess established in a ceramic object. In this situation, the space between the surface of the metal object and the ceramic surface defining the recess inhibits the removal of oxygen, even when a vacuum furnace and flux are utilized. Consequently, a reliable braze joint cannot be established between the metal object and the ceramic surface defining the recess.
A specific application where this problem arises is in mass spectrometers that include a ceramic housing with a hollow interior where a low-pressure or vacuum environment is maintained and various electrical components are located. The electrical components located within the housing must be connected to control and/or processing circuitry located exterior to the housing. To achieve such a connection and preserve the vacuum environment, one or more holes must be established between the exterior of the housing and the interior of the housing, a distance that is typically an inch or more, and a solid metal pin that is capable of conducting the necessary signals must be brazed to the ceramic surface defining the hole. Due to the length of the hole and the relatively small clearance between the metal pin and the surface of the ceramic surface defining the hole, there is a high degree of resistance to the establishment of an oxygen depleted environment adjacent to the surface of the metal pin and the ceramic surface defining the hole. Consequently, the reliability of any braze joint subsequently established between the surfaces using only a vacuum furnace and a flux is questionable. Moreover, to reduce undesirable magnetic effects on the operation of the mass spectrometer, the metal pin is made of titanium, which is a non-magnetic material. Unfortunately, titanium has a high affinity for oxygen that makes the establishment of the requisite oxygen depleted atmosphere even more difficult.
Based on the foregoing, there is a need for a process that allows a metal object to be brazed to a ceramic surface that defines a recess for receiving the metal object where the space between the metal object and the ceramic surface provides substantial resistance to the establishment of the oxygen depleted environment necessary to produce a reliable braze joint. The need for such a process is especially noticeable where the metal object is made of titanium.